1. Field of the Invention
The present invention relates to an alkaline dry battery and a sealing gasket therefor, and is effective, for example, for applying to a cylindrical alkaline dry battery of LR6 type (AA), LR03 type (AAA), or the like.
2. Description of the Related Art
A cylindrical alkaline dry battery of a type such as LR6, LR03, for example as disclosed in Japanese Patent Application Laid-Open Publication No. H11-250875 (hereinafter referred to as “Reference 1”), has an alkaline power generation element consisting of a cathode mixture, a separator, and a anode mixture contained in a cylindrical metallic battery case with a closed bottom, and an opening of the battery case is sealed in an airtight manner using a resin gasket.
The power generation element in which a tubular separator impregnated with an alkaline electrolyte is placed inside of a tubular molded cathode mixture, and a gelled anode mixture is filled inside of this separator. The battery case serves as both a cathode current collector and a cathode terminal by directly contacting the cathode mixture. Inside of the anode mixture, a metallic anode current collector in a bar shape is inserted. This anode current collector is fixed by welding upright on an internal surface of the dish-shaped metallic anode terminal plate. The anode terminal plate, the anode current collector, and the sealing gasket are preassembled together, and they become a sealing unit that closes an opening of the battery case.
The sealing gasket is an integrated molding product of polyamide resin and its perimeter part is disposed between the battery case and the anode terminal plate, and forms an airtight seal therebetween by stress deformation (elastic deformation) caused by flexing the opening of the battery inwardly.
In the alkaline dry battery of Reference 1, a metallic stiffening member is placed between the anode terminal plate and the gasket to achieve a desired configuration for ensuring the airtight sealing condition. This stiffening member is also called as a supporting member or a neutral ring. The perimeter part of the gasket is strongly pressed (crimped) between the stiffening member and the battery case opening and subject to stress deformation. At this time, the stiffening member works as a supporting member for strongly crimping the perimeter part of the gasket and for shape retaining that prevents development of stress distortion or deformation to the entire gasket by its partial crimping.
In this manner, a configuration of providing the stiffening member to the sealing gasket is effective for ensuring the sealing effect by the stress deformation of the perimeter part of the gasket, and is generally adopted by the alkaline dry batteries other than disclosed in Reference 1.
In this case, a shape/structure of the sealing gasket is determined with taking the use of the stiffening member into account. In terms of material of the sealing gasket, many kinds of polyamide series resin are disclosed and listed without specific notes, for example, in Japanese Patent Application Laid-Open Publication No. H09-27305 (hereinafter referred to as “Reference 2”). However, when the use of stiffening member is premised, the difference between the kinds of resin disclosed therein does not cause any particular difference that significantly relates to performance of the alkaline dry battery even though there would some specific difference of resin such as moldability or general physical property. This is presumed that the use of the stiffening member compensates the difference between the kinds of resin.
As described above, many of conventional alkaline dry batteries are configured to employ the stiffening member to the resin sealing gasket made of polyamide or the like for achieving the sealing structure that prevents leakage of alkaline electrolyte.
However, the use of the stiffening member causes a problem which increases a cost because of increase in number of parts and assembly steps. Further, the increase in number of parts creates a problem in which a number of portions increase that could cause failure.
For these reasons, the present inventors have been seeking for many years the alkaline dry battery having a unique sealing structure that can dispense with use of the stiffening member. This unique sealing structure has been applied to actual products and achieved satisfactory results.
In the cylindrical alkaline dry battery of a type such as LR6 or LR03, the unique sealing structure different from the structure essentially requiring stiffening, use of the stiffening member is necessary for obtaining a required sealing effect to prevent leakage of the alkaline electrolyte with only the sealing gasket and not using the stiffening member. This sealing structure with the unique configuration (with no stiffening structure) utilizes a sealing gasket 30′ of a shape/structure as shown in FIG. 3.
FIG. 3 shows a cross section of an alkaline dry battery 10′ that has been resulted from a research by the inventors and practically applied prior to the present invention. The sealing gasket 30′ used in the alkaline dry battery 10′ is an integrated molding product of a polyamide resin (Nylon66), and has a central boss 31, a perimeter part 32, a middle barrier 33, a safety valve, and a stress absorbing part by thin wall parts 35 and 36. The central boss 31 is a part through which an anode current collector 25 is inserted, the collector 25 being arranged upright by welding on a dish-shaped metallic anode terminal plate 40.
The perimeter part 32 is a circular part sandwiched and supported between an opening 16 of a battery case 15 and a peripheral part 42 of the anode terminal plate 40, and forms an airtight sealing condition by stress deformation (elastic deformation) caused by flexing the opening 16 of the battery case 15 inwardly.
A safety valve is a part that relieves an internal pressure by breaking beforehand when an internal pressure of the battery case 15 abnormally increases, and is formed with the first thin wall part 35 provided in the circular part between the boss 31 and the barrier 33. In the anode terminal plate 40 is provided a small opening 41 for releasing a gas.
A stress absorbing part is defined with the second thin wall part 36 formed by bending the circular part between the perimeter part 32 and the barrier 33, and absorbs the stress deformation or distortion caused when the perimeter part 32 is pinched and pressed between the battery case opening 16 and the anode terminal plate peripheral part 42, that would affect to a part other than the perimeter part 32.
The sealing gasket 30′ of the above structure can achieve a sealing effect equivalent to when using the stiffening member even when the stiffening member is not actually used.
For the sealing gasket 30 of this non-stiffening type, as a result of numerous studies by the inventors, they have reached to obtain the following facts for improving reliability of safety valve operation and anti-leakage performance.
In other words, according to the facts found by the inventors, in the gasket 30′ of the non-stiffening type, even when the resin used in the structural material is the same polyamide resin, it is revealed that the reliability of the safety valve operation and the anti-leakage performance can distinctively differ according to a kind of resin selected among the species of resin in a polyamide resin as a genus. In other words, it is revealed that the reliability of the safety valve operation and the anti-leakage performance can be particularly improved by constructing the sealing gasket of the non-stiffening type, which does not use the stiffening member, with the specific kind of polyamide resin.
The polyamide resin demonstrating this distinctive effect is polyhexamethylene dodecanamide called Nylon 612 (trade mark), and is proved to bring the distinctive change (effect) to the reliability of the safety valve operation and the anti-leakage performance only when it is used in combination with the above-mentioned shape/structure with non-stiffening structure.
This polyhexamethylene dodecanamide is, conventionally, disclosed as one of a polyamide type resin group without noting specific preference to such use, for example, in References 1 and 2, or the like. However, the relationship of the reliability of the safety valve operation and the anti-leakage performance in the alkaline dry battery with the kind of the resin used is not disclosed. From References 1 and 2, it can be speculated that polyhexamethylene dodecanamide which is one kind of polyamide resin can be replaced with polyhexamethylene adipamide (Nylon 66) or the like, but there is no disclosure that suggests the difference over the effect that relates to the reliability of the safety valve operation and the anti-leakage performance in the alkaline dry battery.
In addition, the sealing gasket of non-stiffening type which is in combination with the sealing structure using the stiffening member does not bring the distinctive effect to the reliability of the safety valve operation and the anti-leakage performance. Polyhexamethylene dodecanamide (Nylon 612) brings the effect of distinctively improving the reliability of the safety valve operation and the anti-leakage performance only in combination with the shape/structure that does not use the stiffening member, and this effect is revealed by the inventors as described above.